1. Field of the Invention
The invention relates to an inkjet printer that has a station type ink supply system in which a main tank and a sub-tank are capable of being connected to, and disconnected from, each other. The main tank and the sub-tank are connected to each other when ink is supplied from the main tank to the sub-tank.
2. Description of Related Art
In an inkjet printer, a printhead (ejecting head) ejects a droplet of ink onto a sheet of recording media to form an image. Japanese Laid-Open Patent Publication No. 2003-175588 discloses an inkjet printer in which a main tank and a printhead are constantly connected to each other using a tube such that ink is supplied from the main tank to the printhead.
In a printhead of an inkjet printer, a droplet of liquid, such as ink is ejected from a nozzle by a piezoelectric element when the piezoelectric element deforms. The droplet of ink may also be ejected from the nozzle by a heat-generating resister when that heat generating element volumetrically changes an air bubble. Usually, the nozzle is not provided with a valve. Rather, a meniscus is formed in the nozzle in a concave manner inwardly from the nozzle surface so that no ink leaks from the nozzle when the printhead is in stand-by mode.
The nozzle is a small opening. Accordingly, liquid in the nozzle forms a dome-shaped meniscus therein due to surface tension. The meniscus is concave when the pressure inside the nozzle is less than the atmospheric pressure. Such a meniscus prevents the liquid from leaking from the nozzle when the printhead is in stand-by mode.
In an inkjet printer in which the main tank and the printhead are constantly connected to each other, the ink level in the main tank is disposed so as to always be lower than a nozzle surface of the printhead. As a result, the pressure inside the nozzle is maintained at less than the atmospheric pressure.
A color inkjet printer, which forms a multicolor image by overlapping inks of basic colors, includes a plurality of main tanks corresponding to basic ink colors.
Each main tank of the color inkjet printer has a relatively small width compared to the other dimensions of the main tank. The main tanks are arranged in a horizontal direction such that the width of each main tank extends in the horizontal direction so that the height difference between each main tank and the printhead is the same.
In order to improve image quality, it is necessary to increase the number of basic ink colors. However, increasing the number of basic ink colors increases the number of main ink tanks. If the number of main tanks is increased in the inkjet printer, the dimension in the horizontal direction of a mounting space for the main tanks is increased.
In the case where ink meniscuses are maintained by the height difference between the ink level in the main tank and the printhead, the main tank needs to be mounted at a position low enough with respect to the printhead to ensure a sufficient height difference even when the main tank holds therein a large amount of ink or when the ink level in the main tank is high.
Inkjet printers have been downsized to meet the recent demands from the market. If a main tank is mounted at a position low enough with respect to a printhead of a compact inkjet printer, the main tank becomes positioned close to a mounting surface for the inkjet printer. In this case, when the user inserts or removes the main tank, the mounting surface might interfere with the user's hand.
In view of the forgoing problem, it is an object of the invention to provide a compact inkjet printer that allows easy access to main tanks, without increasing a dimension in a horizontal direction of a mounting space for the main tanks.